Microstrip Antenna : Construction, Working, Types, Feeding Methods & Its Applications

An antenna or aerial in radio engineering is a specialized transducer, designed by an array of conductors which are connected electrically to the transmitter or receiver. The main function of an antenna is to transmit & receive radio waves equally within all horizontal directions Antennas are available in different types and shapes. The small antennas can be found on the roof of homes to watch TV and big antennas capture signals from different satellites which are away millions of miles. Antennas move vertically & horizontally to capture & transmit the signal. There are different types of antennas available like aperture, wire, lens, reflector, microstrip, log periodic, array, and many more. This article discusses an overview of microstrip antenna.

Microstrip Antenna Definition

An antenna that is shaped by simply etching out a piece of conductive material above a dielectric surface is called a microstrip antenna or a patch antenna. On the ground plane of this microstrip antenna, the dielectric material is mounted, where this plane supports the entire structure. In addition, the excitation to this antenna can be provided with feed lines that are connected to the patch. Generally, these antennas are considered low-profile antennas that are used in microwave frequency applications that have above 100 MHz frequency.

Antenna’s micro-strip/patch can be selected to be rectangular, square, elliptical & circular for ease of analysis and fabrication. Some microstrip antennas do not utilize a dielectric substrate but they are made with a metal patch that is mounted on a ground plane with dielectric spacers; thus the resulting formation is less strong but its bandwidth is wider.

Microstrip Antenna Construction

Microstrip antenna design can be done with the help of an extremely thin metallic strip by arranging it on a ground plane in between a dielectric material. Here, the dielectric material is a substrate used for separating the strip from the ground plane. Once this antenna is excited, then the generated waves in the di-electric undergo reflections & the energy emitted from the metal patch edges is very low. These antenna shapes are identified by the metallic patch shape arranged on the dielectric material.

Generally, the strip/patch & the feed lines are photo-etched on the surface of the substrate. There are different microstrip antenna shapes like square, dipole, rectangular, circular, elliptical, and dipole. We know that patches can be formed in various shapes but, because of the easy in fabrication, circular, square & rectangular shaped patches are normally used.

Microstrip antennas can also be formed with a group of various patches above a dielectric substrate. Either single or numerous feed lines are utilized to give excitation to the microstrip antenna. So the presence of microstrip element arrays provides better directivity, high gain, and increased range of transmission with low interference.

Working of Microstrip Antenna

A microstrip antenna works as; whenever current throughout a feed line arrives at the microstrip antenna’s strip, then electromagnetic waves are produced. So these waves from the patch will start radiating from the width side. However, when the strip thickness is very small, the waves produced in the substrate will get reflected through the strip edge. The constant strip structure along the length does not allow radiation emission.

The microstrip antenna’s low radiating capability allows for covering only wave transmissions with small distances like stores, indoor locations, or local offices. So this inefficient wave transmission is not acceptable in a centralized locality in a very large area. Usually, hemispherical coverage is given by a patch antenna at a 30⁰ – 180⁰ angle at a distance from the mount.

Microstrip Antenna Specifications

The microstrip antenna specifications include the following.

• Its resonant frequency is 1.176 GHz.
• The frequency range of the microstrip antenna is from 2.26 GHz to 2.38 GHz.
• The substrate’s Dielectric constant is 5.9.
• The dielectric substrate’s height is 635um.
• The feeding method is a microstrip line feed.
• The loss tangent is 0.00 12.
• The conductor is silver.
• The thickness of the conductor is 25um.
• Its Bandwidth is fo ± 10 GHz.
• Its gain is above 5dB.
• Its axial ratio is below 4dB.
• Its return loss is better than 15dB.

Microstrip Antenna Types

There are different types of microstrip antennas available which are discussed below.

Microstrip Patch Antenna

These types of antennas are low-profile antennas where a metal patch is arranged at ground level through a dielectric material in-between comprising a strip (or) Patch Antenna. These antennas are extremely low size antennas with low radiation. This antenna includes a radiating patch on one face of a dielectric substrate and on the other side, it has a ground plane.

Generally, the patch is made with conducting material like gold or copper. These types of antennas can be formed with a microstrip method by simply fabricating on a PCB. These antennas are used in microwave frequency applications which have greater frequency than 100 MHz.

Microstrip Dipole Antenna

The microstrip dipole antenna is a thin microstrip conductor and is placed on the actual part of the substrate & it is covered totally with metal on one face known as the ground plane. These antennas are used in digital communication devices like computers & the nodes for WLAN. The width of this type of antenna is small so it can be utilized at the entrée point of the WLAN system.

Printed Slot Antenna

Printed slot antenna plays a key role in enhancing the antenna’s bandwidth with radiation patterns in both directions. This antenna’s sensitivity is low as compared to the normal antennas. These antennas are required throughout a feed line which is arranged reverse to the substrate & vertically to the slot axis provided above the patch.

Microstrip Travelling Wave Antenna

Microstrip traveling wave antennas are mainly designed with a long Microstrip line by sufficient width for supporting the TE connectivity. These types of microchip antennas are designed in such a way that the major beam lies within any route from broadside to end fire.

Feeding Methods of Microstrip Antenna

The microstrip antenna has two feeding methods; contacting feed and noncontacting feed which are discussed below.

Contacting Feed

The power in contacting feed is provided directly to the radiating element. So this can be done with a coaxial line/microstrip. This type of feeding method is again classified into two types; Microstrip feed and coaxial feed which are discussed below.

Microstrip Feed

Microstrip feed is a conducting strip with a very small width than the radiating element’s width. The feed line provides simple etching above the substrate because of the strip has thinner dimensions. The benefit of this type of feed arrangement is; that the feed can be etched on top of a similar substrate to offer a planar structure. The feed line toward the structure is provided either at the middle, offset, or inset. The main purpose of the inset cut within the patch is to match the impedance of the feed line’ to the patch without requiring any extra matching element.

Coaxial Feed

This feeding method is the most frequently used type and is a non-planar feeding method where z co-axial cable is used for feeding the patch. This feeding method is given to the microstrip antenna in such a way that the inside conductor is directly connected to the patch whereas the external conductor is connected to the ground plane.

The impedance will change with the difference in the arrangement of the coaxial feed. Once the feed line is connected anyplace in the patch thus helps impedance matching. However, the feed line connecting throughout the ground plane is a bit hard because this will need drilling a hole within the substrate. This feeding method is very simple to fabricate & has less spurious radiation. But, its main drawback is that it is connected to a ground plane connector.

Non-contacting Feed

The power is given to the radiating element from the feed line with electromagnetic coupling. These feed methods are available in three types; aperture coupled, proximity coupled, and branch line feed.

Aperture Coupled Feed

The aperture feed technique includes two dielectric substrates like antenna dielectric substrate, & a feed dielectric substrate which are divided simply through a ground plane and have a gap in the middle. The metal patch is located above the substrate of the antenna whereas the ground plane is located on another face of the antenna dielectric. To provide isolation, the feed line and feed dielectric are located on another side of the ground plane.

This feeding technique provides an outstanding polarization purity which is unachievable by other feed techniques. Aperture couple feed provides high bandwidth and is extremely helpful in applications where we don’t want to utilize wires from single layer to another. The main drawback of this feeding technique is, it needs multilayer fabrication.

Proximity Coupled Feed

Proximity-coupled feed is also called indirect feed where the ground plane is not present. As compared to an aperture-coupled feed antenna, it is very simple to manufacture. On the conductive face of the antenna, a slot is there & coupling is given with a microstrip line.

This feeding method provides low spurious radiation & a huge bandwidth. The feed line in this method is located between two dielectric substrates. The feed line edge is arranged at some point wherever the input impedance of the microstrip antenna is 50 ohms. This feeding technique has enhanced bandwidth efficiency as compared to the other types of methods. The main drawback of this technique is; that multilayer fabrication is possible & it provides poor polarization purity.

Branch Line Feed

In the branch line feed technique, a conducting strip is directly connected to the patch edge of the microstrip. As compared to the patch, the width of the conducting strip is smaller. The main benefit of this feeding technique is; that the feed is etched on a similar substrate to give a planar structure.

An inset cut can be integrated into the patch to get excellent impedance matching without the requirement of any extra matching element. This can be attained by controlling the inset position properly, otherwise, we can slice the slot & etch it from the patch with a suitable size. Furthermore, this feeding technique is utilized & called as branch line feed technique.

Microstrip Antenna Radiation Pattern

The graphical representation of the antenna’s radiation properties is known as radiation pattern which explains how the antenna emits energy into space. The variation in the power as an arrival angle’s function is monitored in the far field of the antenna.

The microstrip antenna radiation pattern is broad and it has less radiation power & narrow frequency BW. The microstrip antenna’s radiation pattern is shown below which lesser directivity has. By using these antennas, an array can be formed to have a superior directivity.

Characteristics

The microstrip antenna characteristics include the following.

• The microstrip antenna patch should be an extremely thin conductive region.
• As compared to a patch, the ground plane should have fairly extremely large dimensions.
• Photo-etching on the substrate is done to construct the radiating element & feed lines.
• A thick dielectric substrate by the dielectric constant in the 2.2 to 12 range offers excellent performance of an antenna.
• Microstrip element arrays in the microstrip antenna design offer superior directivity.
• Microstrip antennas offer high beam width.
• This antenna provides extremely high-quality factors because a high Q factor results in a low efficiency & slight bandwidth. But, this can be compensated by simply increasing the width of the substrate. However, the increase in width beyond a particular limit will cause an unnecessary power loss.

Advantages and Disadvantages

The advantages of microstrip antenna include the following.

• Microstrip antennas are very small.
• These antenna’s weight is less.
• The fabrication procedure provided by this antenna is simple.
• Its installation is very easy because of its small size & volume.
• It offers simple integration by other devices.
• This antenna can perform double & triple-frequency operations.
• These antenna arrays can be constructed easily.
• This antenna provides a high amount of robustness above strong surfaces.
• It is simple to fabricate, customize & modify..
• This antenna has simple and low-cost construction.
• In this antenna, linear & circular polarization is achievable.
• It is appropriate for array antennas.
• It is compatible with monolithic microwave ICs.
• Bandwidth can be expanded by simply improving the width of dielectric material.

The disadvantages of microstrip antennae include the following.

• This antenna provides less gain.
• The efficiency of this type of antenna is low due to conductor & dielectric losses.
• This antenna has a high range of cross-polarization radiation.
• The power handling capacity of this antenna is low.
• It has less impedance bandwidth.
• The structure of this antenna radiates from feeds & other junction points.
• This antenna shows extremely sensitive performance towards ecological factors.
• These antennas are more prone to forged feed radiation.
• This antenna has more conductor & dielectric losses.

Applications

The uses or applications of microstrip antennae include the following.

• Microstrip antennas are applicable in different fields; in missiles, satellites, space crafts, aircraft, wireless communication systems, mobile phones, remote sensing & radars.
• These antennas are used in wireless communications. to show compatibility with handheld devices such as mobile phones & pagers.
• These are used on missiles as communication antennas.
• These antennas have a small size, so used in microwave and satellite communication applications.
• GPS is one of the main benefits of microstrip antennas because it provides ease within vehicles & marines tracking.
• These are used in phased array radars to handle bandwidth tolerance equal to some percentage.

How to Improve the Bandwidth of Microstrip Antenna?

The bandwidth of a microstrip antenna can be enhanced by different techniques like enhancing the substrate thickness with low dielectric constant, slot cutting, probe feeding through notches cutting & different forms of antenna

Why Do Microstrip Antennas Radiate?

Microstrip patch antennas radiate mainly due to the fringing fields among the patch edge & the ground plane.

How to Increase the Gain of Microstrip Antenna?

The gain of the microstrip antenna can be increased with a parasitic patch & air gap in between the feed patch & ground plane.

Thus, this is an overview of microstrip antenna, working & its applications. This antenna is quite a modern invention that allows convenient integration of an antenna & other driving circuitry of a communication system on a common PCB (or) a semiconductor chip. These are extensively used in an extensive range of current microwave systems in the range of gigahertz. The main benefits of this antenna are; lightweight, low cost, conformal shapes & compatibility with the monolithic & hybrid microwave ICs. Here is a question for you, What is a dipole antenna?